In the Integral Water Cycle, aquifers have a key function. In this sense, rainwater infiltrates the ground, occupying pores and cracks in the subsoil, giving rise to underground runoff. The water is stored in aquifers and is susceptible to being exploited through catchment works to satisfy human needs. The lack of control over these catchment activities generates great pressure on these formations and their operation, so that the natural recharge of the aquifers can be modified, changing the spatio-temporal patterns of availability of water resources. To avoid these impacts, it is important to know the dynamics and characteristics of these water storage systems.
In this Green Ecologist article you can discover what aquifers are and how an aquifer is formed, but we will focus more on knowing which are the different types of aquifers that exist.
What is an aquifer and how many types are there
Aquifers are geological formations with hydraulic properties that allow the storage and free transmission of water through its pores or cracks. Between the parts of an aquifer, can be distinguished:
- The water table.
- The saturation zone.
- The waterproof layer.
The underground water It is located in the saturation zone, below the water table, which constitutes the upper limit of this zone. The greater the depth of the saturated zone, the greater the water pressure. Since stored water flows to areas of lower pressure, it naturally emanates to the surface through upwelling (coals), springs, springs or river beds. In addition, depending on the type of aquifer, there is an impermeable area that prevents the passage of water.
The aquifer recharge it takes place through the infiltration-percolation process of precipitated water. It involves: gravity and lithology.
- On the one hand, gravity is the force that draws water towards the center of the earth, allowing it to circulate vertically, from the earth's surface to the different depths of the subsoil.
- On the other hand, lithology determines the degree of porosity or compaction of the geological materials that make up the aquifer. Depending on this, the water can accumulate and circulate more or less easily.
If you want to know in more detail what an aquifer is and how it is formed, here is another summary of Ecologista Verde. There are different criteria for classify aquifers that exist. Four types of classifications are established in this article.
Classification according to hydrogeology
Depending on the lithological behavior compared to groundwater, 4 are differentiated hydrogeological systems: aquifers, aquitards, aquicluids and aquifuges.
- According to its geological formations, aquifers They can be considered excellent (made up of clean gravels), fair-good (made up of clean sands, gravels and sands or fine sand) or poor (fine sand, silty sand and fractured limestone) for the storage and transmission of groundwater. In general, this system is characterized by a high capacity to store, drain and transmit water.
- The aquitards, formed by silts, silty sands and clays, have a high capacity to store water but present problems for its drainage (medium-low capacity) and its transmission (low capacity). It is an intermediate term between what is an aquifer and an aquicluid.
- The characteristic formations of aquicluids Despite having a high porosity, they are impervious to the passage of water (marl, clay or pumice stone). Therefore, its storage, drainage and transmission capacity is nil.
- The aquifuges They are geological formations that cannot store or transmit water. Some examples are igneous rocks that are neither fissured nor fractured. Here you can learn more about the types of igneous rocks and their characteristics.
Classification according to hydraulic pressure level or aquifer pressure
The location of the aquifers, their hydrological behavior and the characteristic geology, give rise to three types of aquifers different: free, confined and semi-confined.
- Free, unconfined or groundwater aquifers they do not present impermeable formations. In them, the unsaturated zone is located between the ground surface and the water table and the water is in contact with air and at atmospheric pressure.
- Confined, Captive, Pressure, or Charged AquifersUnlike free aquifers, they are not in contact with the atmosphere due to the presence of impermeable or confining materials. In a captive or confined aquifer, the water completely saturates the pores or cracks, so that when drilling it rises until the hydraulic pressure is balanced with the atmospheric one.
- Semi-confined aquifersThey are also pressurized aquifers, like the confined ones, but unlike the latter, there is greater permeability in them (they are considered aquitards).
According to lithological characteristics
The lithology allows to distinguish two types of aquifers: detrital and carbonate (or karst):
- Detrital aquifersThey are free aquifers in contact with rivers, which are formed mainly by clay materials, very little permeable. They may also contain accumulations of highly permeable and porous detrital materials, sand and gravel. This makes its permeability variable.
- Karst or carbonate aquifers They are made up of limestone and dolomatic materials, which allow the accumulation of rain and runoff, due to their dissolution (high permeability).
Image: Google Sites Aquifer Mantos
According to texture
According to the properties of its texture, aquifers can be: porous or fissured.
- In porous aquifers the water saturates the pores, interconnected, which confers permeability and capacity to transmit water. This varies depending on the training material.
- In fissured aquifers, the water is located in the fissures of the rocks, which are also communicated. The circulation of water, being cracks and not pores, is less predictable and more heterogeneous.
Now that you know the different classifications of the types of aquifers, we encourage you to learn more about inland waters: what they are, characteristics and importance with this other article by Green Ecologist.
If you want to read more articles similar to Types of aquifers, we recommend that you enter our category of Other environment.
